It is well known to those skilled in the art that foamed plastic surfaces may be textured by the process commonly referred to as "chemical embossing", wherein the surface of a foamable polymer composition is printed with an ink composition containing an agent which inhibits foaming in the printed areas when the foamable polymer composition is subsequently subjected to a heat treatment. The areas which have not been printed over thus expand normally on heating while expansion in the printed areas containing the inhibitor is retarded, resulting in a textured surface with depressions in those areas printed with the inhibited ink.
A wide range of compounds have been claimed to act as inhibitors for chemical embossing of floor and wall covering surfaces. Carboxylic acid anhydrides such as trimellitic anhydride (TMA), disclosed in Nairn et al. U.S. Pat. No. 3,293,094, being among the most commonly used industrially. However, compounds such as TMA, while suitable for solvent-based printing inks, are hydrolytically unstable and thus are not readily usable in the aqueous ink formulations which are rapidly gaining in importance in large scale printing operations due to environmental concerns over VOC (volatile organic compound) emissions from solvent-based inks.
Triazole compounds such as benzotriazole (BTA) and tolyltriazole (TTA) are also widely used in solvent-based inks for chemical embossing. These compounds do not hydrolyze on contact with water as do carboxylic acid anhydrides like TMA. However their use in aqueous ink systems is hindered by a lack of substantial water solubility.
The excellent embossing characteristics, stability and low toxicity of the aromatic triazoles have prompted considerable research into ways that these compounds could be successfully adapted to aqueous ink systems. The prior art, specifically Hamilton U.S. Pat. No. 4,083,907 and Hamilton U.S. Pat. No. 4,191,581, has established that sufficient BTA or aminotriazole for acceptable embossing can be solubilized into an aqueous ink by addition of a water soluble alcohol and buffering agents to raise the pH of the ink formulation to between 8-12.
Certain carboxylic acids, acid anhydrides and acid halides have also been claimed to act as foam-expansion inhibitors in aqueous ink formulations where the acidic species have been neutralized and the formulation pH adjusted to the same 8-12 range (Brixius U.S. Pat. No. 4,369,065 and Brixius U.S. Pat. No. 4,421,561).
Benzotriazole and other inhibitor species have also been solubilized in alcohol-containing aqueous inks where the system pH is in the acidic range from 3-5 (Sherman et al. U.S. Pat. No. 5,169,435).
Modified aromatic azole derivatives have also been cited as foam-expansion inhibitors. These compounds are substituted on the 1-N of the triazole or imidazole ring with dialkylaminomethyl groups of varying structure and are claimed to be easily incorporated into aqueous inks which contain alcohols or other water soluble organic solvents, and do not require the use of a pH regulator (Hauser et al. U.S. Pat. No. 4,407,882). Compounds of this general structure in which the alkyl groups of the aminomethyl substituent are simple hydrocarbons (D'Errico U.S. Pat. No. 4,522,785) and perfluoroalkyls (Clark et al. U.S. Pat. No. 4,788,292) have also been claimed as corrosion inhibitors.
Enhancement of the solubility of such derivatives in a wide range of functional fluids of varying polarity have been investigated. Popplewell et al. U.K. Patent No. 1,466,558 discloses mono- and di-(methyl benzo- and naphthoazole) substituted amino corrosion inhibitors.
Synthesis of benzotriazole derivatives is disclosed in Mozilis, V. V. and Jokubaityte, S. P. "The Benzotriazole and Thiourea in Mannich Reaction." Works of the Academy of Sciences of the Lithuanian SSR, Vol. 1(60), (1970) (Chem. Abstr. 70 77152r (1970)); Katritzky, A. R., Pilarski, B. and Urogdi, L. "Reactions of Benzotriazole with Formaldehyde and Aliphatic Primary Amines." J. Chem. Soc., (1990), pp. 541-7; Katritzky, A. R. and Hughes, C. V. "The Chemistry of N-Substituted Benzotriazoles." Chemica Scripta, Vol 29, (1989), pp. 27-31; Katritzky, A. R., Yao, G., Lan, X. and Zhao, X., J. Org. Chem. 1993, 58 2086; Katritzky, A. R., Jurczyk, S., Rachwal, B., Rachwal S., Shcherbakova, I. and Yannakosoulou, K., Synthesis 1992, 1295; and Katritzky, A. R., Rachwal, S. and Rachwal, B., J. Chem. Soc. Perkin Trans I 1987, 799.
Frisch WO 89/04341 suggests directly incorporating benzotriazole or tolyltriazole inhibitors as solid powders into aqueous ink. This approach to chemical embossing is complicated by the slight-to-moderate solubility of these compounds in the variable water/alcohol mixtures routinely found in aqueous ink formulations. Affinity for the solvent can lead to inhibitor particle agglomeration. Interaction with the ink resins/surfactants can cause destabilization (e.g. flocculation) of the pigments and cause ink tack during printing and drying.
As the azole-based foam-expansion inhibitors established in the patent literature to date are either liquids or not soluble in water unless alcohols or other suitably water-miscible organic cosolvents are also present, and do not readily form stable aqueous ink-compatible dispersions, there continues to exist a need in the art for an azole-based inhibitor which can be readily dispersed into an aqueous-based printing ink, both anionic and cationic, without compromising the ink stability or printing characteristics.